This invention relates to a gate circuit, and more particularly to an improvement in a gate circuit which is suitably used for a noise squelch circuit etc.
Conventional noise squelch circuits employ such a gate circuit as shown in FIG. 1. In FIG. 1, numerals 1 and 2 designate emitter follower amplifiers, numeral 3 a gate transistor and character C a capacitor for holding a voltage level. The transistor 3 is normally in its on state and turned off when a noise enters an input S.sub.1 of transistor 1 and a negative noise signal indicating pulse signal P is applied to the base of the transistor 3. Thus, the noise can be removed effectively.
It will be understood that such a pulse signal for controlling the switching of the gate circuit must have a large amplitude. However, as apparent from an equivalent circuit of the gate circuit portion as shown in FIG. 2, the output signal S.sub.2 is subject to undesirable influence by a leakage of the pulse signal if the pulse signal of large amplitude is used for cutting off the transistor 3. The employment of the large amplitude pulse signal will cause low dynamic range of the circuit, high resistance of the transistor when saturated and undesirable frequency characteristics of the circuit. In FIG. 2, D.sub.1 and D.sub.2 are diodes equivalent to the characteristics between the base and collector of the transistor 3 and between the base and emitter thereof, respectively, and SW is an equivalent switch for a short circuit between the base and collector of the transistor 3.
It is an object of the present invention to provide a gate circuit free from any of the disadvantages of the conventional gate circuits as referred to above.